Method and apparatus of forming alignment layer for liquid crystal display device

ABSTRACT

A method for forming an alignment layer is disclosed, to prevent light leakage generated by a physical contact between a rubbing roll and a substrate, which includes preparing a substrate; coating an alignment material on the substrate, for initial alignment of liquid crystal; applying an electric field or a magnetic field to the alignment material, for determination of alignment direction in the alignment material; and curing the alignment material.

This application claims the benefit of Korean Patent Application No.P2005-0011317, filed on Feb. 7, 2005, which is hereby incorporated byreference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display (LCD) device,and more particularly, to an alignment layer for initial alignment ofliquid crystal in an LCD device.

2. Discussion of the Related Art

Among various ultra-thin flat type display devices, which include adisplay screen having a thickness of several centimeters, a liquidcrystal display (LCD) device has great attention because of its widevariety of uses, including notebook computers, monitors, spacecraft,aircraft, and etc.

Generally, the LCD device includes a color filter substrate having acolor filter layer, a thin film transistor substrate having a thin filmtransistor, and a liquid crystal layer formed between the color filtersubstrate and the thin film transistor substrate. At this time, the thinfilm transistor substrate is positioned opposite to the color filtersubstrate.

In the LCD device, an alignment direction of the liquid crystal layer ischanged according to application of voltage, thereby controlling thetransmittance of light. Accordingly, images are displayed in the LCDdevice. For application of voltage, electrodes are formed on the thinfilm transistor substrate and the color filter substrate. That is, apixel electrode is formed on the thin film transistor substrate, and acommon electrode is formed on the color filter substrate, whereby anelectric field is vertically formed between the thin film transistorsubstrate and the color filter substrate (for example, Twisted Nematic(TN) mode). In another method, the pixel electrode and the commonelectrode may be formed on the thin film transistor substrate, therebyforming an electric field parallel to the two substrates (for example,In-Plane Switching (IPS) mode).

FIG. 1 is an exploded perspective view of a TN mode LCD device accordingto the related art. As shown in FIG. 1, a thin film transistor substrate10 of the TN mode LCD device according to the related art includes agate line 12, a data line 14, a thin film transistor T, and a pixelelectrode 16. At this time, the thin film transistor T is formed at acrossing of the gate and data lines 12 and 14, and the pixel electrode16 is connected with the thin film transistor T. Also, a color filtersubstrate 20 includes a black matrix layer 22 including black matrixpatterns for prevention of light leakage, a R/G/B color filter layer 24having red, green and blue color patterns, each color pattern providedbetween the black matrix patterns, and a common electrode 25 formed onthe R/G/B color filter layer 24. In this case, an electric field isvertically formed between the pixel electrode 16 of the thin filmtransistor substrate 10 and the common electrode 25 of the color filtersubstrate 20, thereby controlling the alignment direction of liquidcrystal.

Thereafter, the substrates 10 and 20 are attached to each other to formone liquid crystal panel in which a liquid crystal layer is formedbetween the substrates 10 and 20.

In the meantime, when forming the liquid crystal layer between the twosubstrates 10 and 20, regular alignment of liquid crystal molecules isrequired. For this, although not shown, alignment layers are provided onthe thin film transistor substrate 10 and the color filter substrate 20for initial alignment of liquid crystal.

The alignment layer for initial alignment of liquid crystal is generallyformed in a rubbing alignment method.

The rubbing alignment method includes steps of coating a thin filming ofan organic polymer such as polyimide on a substrate, aligning a sidechain of the organic polymer to a predetermined direction by rubbing thecoated organic polymer by rotating a rubbing roll coated with rubbingcloth, and curing the aligned organic polymer.

Accordingly, the liquid crystal is aligned according to the aligneddirection of the side chain of the organic polymer. That is, the movingdirection of the rubbing roll corresponds to the alignment direction ofliquid crystal.

However, the rubbing alignment method has the following disadvantages.

First, when the rubbing cloth is irregular, there may be resulting lightleakage because of improper or no alignment of the liquid crystal.

FIG. 2 is a perspective view of illustrating the problem generated bythe irregular rubbing cloth.

As illustrated in FIG. 2, the elements such as the thin film transistor,the color filter layer and the electrode layer are formed on thesubstrate. Thus, when the rubbing roll 30 coated with the rubbing cloth32 rotates on the elements formed on the substrate 10 or 20, someportion 32 a of the rubbing cloth 32 may be irregular. As a result, theside chain of the organic polymer on the portion of the substrate rubbedwith the irregular portion 32 a of the rubbing cloth 32 is not alignedor not aligned properly. Therefore, there may be the light leakage dueto the irregular alignment of liquid crystal.

Second, when the rubbing cloth does not in contact with the substrate,there may be light leakage.

FIG. 3 is a perspective view illustrating the alignment state of liquidcrystal when the rubbing cloth is not in contact with the substrate.

As explained earlier, electrode layers, such as pixel electrodes and acommon electrode, are formed on a substrate. Due to a step height inelectrode layers formed on a substrate 10, as illustrated in FIG. 3, aregion (region “A”) is formed where a rubbing cloth 32 does not comeinto contact with the substrate 10. In this case, the alignment of aliquid crystal is not uniform in the region (“A”), resulting in lightleakage.

In conclusion, according to a related art rubbing alignment method, whenthe arrangement of a rubbing cloth is non-uniform or a rubbing clothdoes not come into contact with a substrate, rubbing cannot be performedwell, causing the problem of light leakage. Thus, there is a need for anovel liquid crystal alignment method to solve the problems of therelated art rubbing alignment method.

The above-mentioned problems of the related art rubbing alignment methodare attributed to physical contact between a rubbing roll and asubstrate.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method for formingan alignment layer that substantially obviates one or more problems dueto limitations and disadvantages of the related art.

An advantage of the present invention is to provide a method for formingan alignment layer to prevent light leakage caused by physical contactbetween a rubbing roll and a substrate.

Another advantage of the present invention is to provide an alignmentlayer formation unit to prevent light leakage caused by physical contactbetween a rubbing roll and a substrate.

Additional features and advantages of the invention will be set forth inpart in the description which follows and in part will become apparentto those having ordinary skill in the art upon examination of thefollowing or may be learned from practice of the invention. Theobjectives and other advantages of the invention may be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the invention, as embodied and broadly described herein, a method forforming an alignment layer of an LCD device includes steps of preparinga substrate; coating an alignment material on the substrate, for initialalignment of liquid crystal; applying an electric field or a magneticfield to the alignment material, for determination of alignmentdirection in the alignment material; and curing the alignment material.

Instead of a related rubbing alignment method, a method for forming analignment layer according to the present invention uses a field flux(e.g., an electric field or magnetic field) application method whichdoes not require physical contact for a substrate.

At this time, the alignment direction of the alignment material isidentical to the electric field application direction, and isperpendicular to the magnetic field application direction. Accordingly,it is preferable to apply the electric field in the same direction asthe alignment direction of the alignment material. Also, it ispreferable to apply the magnetic field in perpendicular to the alignmentdirection of the alignment material.

The electric field application method may use an electromagnet or ahorseshoe magnet.

The step of applying an electric or magnetic field can be carried out byvarying the direction of the field applied in a direction parallel,perpendicular or diagonal to the X-axis depending on the alignmentdirection of the alignment material. At this time, variation in thedirection of the electric or magnetic field applied can be performed byrotating an electric or magnetic field generator while fixing thesubstrate applied with the alignment material, or rotating the substrateapplied with the alignment material while fixing an electric or magneticfield generator.

The steps of coating the alignment material, applying the electric ormagnetic field, and curing the alignment material are performed insequence, for the decrease of process time.

In another aspect of the present invention, an alignment layer formationunit includes a substrate stage on which a substrate is loaded; anelectric or magnetic field application part, formed in the periphery ofthe substrate stage; and a curing part for curing an alignment materialof the substrate.

The electric field generator may include an anode and a cathode oppositeto the anode through the substrate stage.

The magnetic field generator may be formed in such a manner that ahorseshoe magnet surrounds the substrate stage or a pair of coiledelectromagnets face each other through the substrate stage.

In addition, an alignment layer applicator may be provided before theelectric field generator or the magnetic field generator.

In this case, the substrate stage may be moveable so as to consecutivelymove the substrate to the alignment layer applicator and the electric ormagnetic field generator.

The electric or magnetic field generator may be rotatable so that thedirection of the electric or magnetic field applied can be properlyvaried depending on the alignment direction of the alignment material.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is an exploded perspective view of illustrating an LCD deviceaccording to the related art;

FIGS. 2 and 3 are perspective views of illustrating problems of rubbingalignment according to the related art;

FIGS. 4A to 4D are process diagrams illustrating forming an alignmentlayer of an LCD device according to embodiment of the present invention;

FIGS. 5A to 5C are process diagrams of showing the process for applyingan electric field in an LCD device according to another embodiment ofthe present invention;

FIGS. 6A to 6D are process diagrams illustrating forming an alignmentlayer of an LCD device according to another embodiment of the presentinvention;

FIG. 7 illustrates an alignment layer formation unit according to anembodiment of the present invention;

FIG. 8 illustrates an alignment layer formation unit according toanother embodiment of the present invention; and

FIG. 9 illustrates an alignment layer formation unit according toanother embodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

Hereinafter, a method for forming an alignment layer according to thepresent invention will be described with reference to the accompanyingdrawings. As illustrated in the embodiments described herein, accordingto the present invention, a field flux (e.g., an electric field or amagnetic field) may be applied to an alignment layer to provide analignment direction in accordance with the direction of the field flux.

FIGS. 4A to 4D illustrate forming an alignment layer of an LCD device byapplication of an electric field according to one embodiment of thepresent invention.

First, as illustrated in FIG. 4A, a substrate 100 is prepared. Thesubstrate 100 is one substrate for an LCD device, which may be a thinfilm transistor substrate including a thin film transistor, or may be acolor filter substrate including a color filter layer. In this case,when the substrate is formed of the thin film transistor substrate orthe color filter substrate, elements formed on the substrate may varydepending on the mode of the LCD device.

For example, in the case where the substrate 100 is a thin filmtransistor substrate for a TN (twisted nematic) mode liquid crystaldisplay, gate lines and data lines crossing each other on a transparentsubstrate are formed to define pixel regions; thin film transistorsincluding a gate electrode, a source electrode and a drain electrode areformed at crossings of the gate lines and the data lines; and pixelelectrodes are formed within the pixel regions to connect to the drainelectrode of the thin film transistors.

Further, in the case where the substrate 100 is a thin film transistorsubstrate for an in-plane switching (IPS) mode liquid crystal display,gate lines and data lines crossing each other on a transparent substrateare formed to define pixel regions; thin film transistors including agate electrode, a source electrode and a drain electrode are formed atcrossings of the gate lines and the data lines; pixel electrodes areformed within the pixel regions to connect to the drain electrode of thethin film transistors; and a common electrode is formed substantiallyparallel to the pixel electrodes.

Further, in the case where the substrate 100 is a color filter substratefor a TN mode liquid crystal display, a light-blocking layer is formedon a transparent substrate to prevent light from leaking; agreen/red/blue color filter layer is formed on the light-blocking layer;and a common electrode is formed on top of the color filter layer.

Further, in the case where the substrate 100 is a color filter substratefor an IPS mode liquid crystal display, a light-blocking layer is formedon a transparent substrate to prevent light from leaking; agreen/red/blue color filter layer is formed on the light-blocking layer;and an overcoat layer is formed on top of the color filter layer toplanarize the substrate.

Modifications and variations of the materials and formation methods ofthe constituent elements formed on the substrate 100 will be appreciatedby those skilled in the art.

In addition to a glass substrate, a flexible substrate or a plasticsubstrate can also be used as the transparent substrate.

Since physical contact occurs between a rubbing roll and a substrate inrelated art rubbing alignment methods, the use of flexible substratescauses problems. In contrast, since the method of the present inventionuses a field flux (e.g., an electric field or a magnetic field), nophysical contact is caused, which will be described in detail below.Accordingly, there is no problem in using flexible substrates in thepresent invention.

In the related art rubbing alignment method, it is necessary to coat analignment material and to cure the coated alignment material. In therelated art, the coated alignment material is cured at a hightemperature of about 230° C. Accordingly, if a plastic substrate is usedin the related art rubbing alignment method, the plastic substrate maybe damaged or bent since plastic is very weak in heat.

However, in case of the alignment method according to the presentinvention which uses the electric field, a curing process is performedat a temperature below 100° C. Thus, the plastic substrate which is weakin relatively high heat in related art curing may be used in thealignment method according to the present invention.

Referring to FIG. 4B, an alignment material 200 is coated on thesubstrate. The alignment material 200 may be formed any material ofwhich an alignment direction is determined with application of electricfield. The alignment material 200 may be formed of polymer selected frompolyimide, polyamic acid, polyvinylcinnamate, polyazobenzene,polyethyleneimine, polyvinylalcohol, polyamide, polyethylene,polystylene, polyphenylenephthalamide, polyester, polyurethane, orpolymethylmethacrylate.

Then, as illustrated in FIG. 4C, an electric field E is applied to thealignment material 200 using an electric field generator 300 todetermine the alignment direction of the alignment material 200.

The electric field generator 300 includes an anode 310 and a cathode 320opposite to the anode through the substrate 100 applied with thealignment material 200. The electric field E is applied from the anode310 to the cathode 320 as indicated by an arrow. Although the anode 310and the cathode 320 do not come into contact with the substrate 100 inthe figure, it is preferred that the anode 310 and the cathode 320 comeinto contact with both sides of the substrate 100 in view of theintensity of the electric field applied.

The alignment material 200 is aligned in the direction of electricfield. The electric field may be applied in the same direction as thealignment direction of the alignment material 200.

Accordingly, where it is desired to align the alignment material 200 inthe direction parallel to the x axis, an electric field may be appliedin the direction parallel to the x axis, as illustrated in FIG. 5A.Where it is desired to align the alignment material 200 in the directionperpendicular to the x axis, an electric field may be applied in thedirection perpendicular to the x axis, as illustrated in FIG. 5B. Whereit is desired to align the alignment material 200 in the directiondiagonal to the x axis, an electric field may be applied in thedirection diagonal to the x axis, as illustrated in FIG. 5C.

To vary the direction of the electric field applied, as illustrated inFIGS. 5A to 5C, the electric field generator 300 or the substrate 100may be rotated.

Referring to FIG. 4D, the curing process is performed. After determiningthe alignment direction of the alignment material 200 by application ofthe electric field, the alignment material 200 is cured, whereby thealignment direction of the alignment material 200 is fixed.

The curing process is performed by applying heat, wherein a temperaturefor the curing process may be varied according to the kind of thesubstrate applied. As mentioned above, if using the plastic substrate,the curing process may be performed at a temperature below about 100° C.

Coating the alignment material 200 (shown in FIG. 4B), applying theelectric field (shown in FIG. 4C), performing the curing process (shownin FIG. 4D), may be performed consecutively thereby decreasing theprocess time.

FIGS. 6A to 6D are process diagrams schematically illustrating formingan alignment layer for a liquid crystal display by application of amagnetic field according to another embodiment of the present invention.

First, as illustrated in FIG. 6A, a substrate 100 is prepared.

Constituent elements that can be formed on the substrate 100 may varydepending on the mode of liquid crystal displays, as in the previousembodiment. In addition to a glass substrate, a transparent substrate,such as a flexible substrate or a plastic substrate, can be used in thepresent invention.

Then, as illustrated in FIG. 6B, an alignment material 200 is applied tothe substrate.

The kinds of the alignment material 200 are the same as those describedin the previous embodiment.

Then, as illustrated in FIG. 6C, a magnetic field B is applied to thealignment material 200 using a magnetic field generator 400 or 500 todetermine the alignment direction of the alignment material 200.

The magnetic field B can be applied using an electromagnet system inwhich a pair of electromagnets 400 wound with coils 420 are arranged toface each other through the substrate, as illustrated in FIG. 6C(1), ora horseshoe magnet surrounding the substrate as illustrated in FIG.6C(2), but the present invention is not limited thereto.

In case of the previous embodiment of the present invention, theelectrodes of the electric field generator may be connected to thesubstrate when applying the electric field. Such process requires anadditional step for connecting the electrode part to the substrate. Incase of the present embodiment of the present invention, it isunnecessary to provide an additional process for connecting an magneticfield application part to the substrate. Thus, the process of applyingthe magnetic field may provide a greater yield than the process ofapplying the electric field.

Since the alignment material 200 is aligned in the directionperpendicular to the direction of the magnetic field applied, themagnetic field may be applied in the direction perpendicular to thealignment direction of the alignment material 200.

To vary the direction of the magnetic field applied, the magnetic fieldgenerator 400 or 500 or the substrate 100 may be rotated.

After that, as shown in FIG. 6D, a curing process is performed.

The curing process is performed by applying heat, wherein a temperaturefor the curing process may be varied according to the type of thesubstrate used. As mentioned above, if using a plastic or flexiblesubstrate, the curing process may be performed at a temperature belowabout 100° C.

Coating the alignment material 200 (shown in FIG. 6B), applying themagnetic field (shown in FIG. 6C), and performing the curing process(shown in FIG. 6D) may be performed consecutively thereby decreasing theprocess time.

FIG. 7 schematically illustrates an apparatus for forming an alignmentlayer for a liquid crystal display by application of an electric fieldaccording to one embodiment of the present invention.

The alignment layer formation unit is provided with a substrate stage600, an electric field generator 300, and a curing part 800. At thistime, a substrate is put on the substrate stage 600, and the electricfield generator 300 is formed at the periphery of the substrate stage600. Also, the curing part 800 is provided to cure an alignmentmaterial.

The electric field generator 300 includes an anode 310 and a cathode 320opposite to the anode through the substrate stage 600. An electric fieldis applied to a substrate 100 securely mounted on the substrate stage600. Before the application of the electric field, an alignment material200 is applied to the substrate 100.

The electric field 300 may be rotated according to the alignmentdirection of the alignment material 200.

The curing part 800 may include a heater which emits heat to thealignment material 200.

Also, an alignment layer applicator 700 may be arranged before theelectric field generator 300. The alignment layer coating part 700 maybe a printing system but it is not limited to this.

In this case, the substrate stage 600 having the substrate 100 isconsecutively moved through the alignment layer applicator 700, theelectric field generator 300, and the curing part 800.

FIGS. 8 and 9 schematically illustrate apparatuses for forming analignment layer for a liquid crystal display by application of amagnetic field according to another embodiment of the present invention.

The alignment layer formation unit is provided with a substrate stage600, magnetic field generators 400 and 500, and a curing part 800. Atthis time, a substrate is put on the substrate stage 600, and themagnetic field generators 400 and 500 are provided at the periphery ofthe substrate stage 600. Also, the curing part 800 is provided to curean alignment material.

The magnetic field generator may be an electromagnet system 500 in whicha pair of electromagnets 400 wound with coils 420 are arranged to faceeach other through the substrate as illustrated in FIG. 8, or ahorseshoe magnet 500 surrounding the substrate as illustrated in FIG. 9,but the present invention is not limited to these structures. Anyapparatus can be used so long as it can generate a magnetic field.

The magnetic field generator 400 or 500 may be rotatable so that thedirection of the magnetic field applied can be properly varied dependingon the alignment direction of the alignment material.

The curing part 800 may include a heater which emits heat to thealignment material 200.

Also, an alignment layer application 700 may be arranged before themagnetic field generators 400 and 500. The alignment layer applicator700 may be a printing system, but it is not limited to this.

In this case, the substrate stage 600 having the substrate 100 may beconsecutively moved through the alignment layer applicator 700, themagnetic field generators 400 and 500, and the curing part 800.

As mentioned above, the method for forming the alignment layer and thealignment layer formation unit according to the related art have thefollowing advantages.

As apparent from the above description, according to the presentinvention, since the alignment direction of an alignment material isdetermined by using a field flux (e.g., an electric or magnetic field),no physical contact with a substrate is required and thus the problem oflight leakage caused by rubbing alignment can be solved.

Also, the curing process for the alignment material may be performed ata temperature below about 100° C. Thus, it is possible to use a plasticsubstrate which is weak in heat, or to use a flexible substrate.

In addition, it is possible to consecutively perform the steps ofcoating the alignment material, applying the electric field or themagnetic field, and curing the alignment material, thereby decreasingthe process time.

By rotation of the electric or magnetic field application part, it ispossible to change the alignment direction of the alignment material.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method for forming an alignment layer of an LCD device comprising: preparing a substrate; coating an alignment material on the substrate, for initial alignment of liquid crystal; applying a field flux to the alignment material, for determination of alignment direction of the alignment material; curing the alignment material by using a heater at a temperature below 100° C., wherein applying the field flux is performed with the field flux application direction parallel to the X-axis, perpendicular to the X-axis, or diagonal to the X-axis depending on the alignment direction of the alignment material, and changing a direction of the field flux by rotating a field flux generator while maintaining the substrate stationary or by rotating the substrate while maintaining the field flux generator stationary.
 2. The method of claim 1, wherein the field flux is an electric field.
 3. The method of claim 2, wherein the electric field is applied in the same direction as the alignment direction of the alignment material when performing the step of applying the electric field.
 4. The method of claim 1, wherein the field flux is a magnetic field.
 5. The method of claim 4, wherein the magnetic field is applied substantially perpendicular to the alignment direction of the alignment material.
 6. The method of claim 4, wherein applying the magnetic field is performed with a pair of coiled electromagnets.
 7. The method of claim 4, wherein applying the magnetic field is performed with a horseshoe magnet.
 8. he method of claim 1, wherein coating the alignment material, applying the field flux, and curing the alignment material are performed in sequence.
 9. The method of claim 1, wherein the step of preparing the substrate includes: defining a pixel region on a transparent substrate by forming gate and data lines crossing each other; forming a thin film transistor at an intersection of the gate and data lines, the thin film transistor including a gate electrode, a source electrode and a drain electrode; and forming a pixel electrode connected with the drain electrode of the thin film transistor.
 10. The method of claim 1, wherein the step of preparing the substrate includes: defining a pixel region on a transparent substrate by forming gate and data lines crossing each other; forming a thin film transistor at an intersection of the gate and data lines, the thin film transistor including a gate electrode, a source electrode and a drain electrode; forming a pixel electrode connected with the drain electrode of the thin film transistor; and forming a common electrode in parallel to the pixel electrode.
 11. The method of claim 1, wherein the step of preparing the substrate includes: forming a black matrix layer on a transparent substrate, for prevention of light leakage; forming an R/G/B color filter layer on the black matrix layer; and forming a common electrode on the color filter layer.
 12. The method of claim 1, wherein the step of preparing the substrate includes: forming a black matrix layer on a transparent substrate, for prevention of light leakage; forming an R/G/B color filter layer on the black matrix layer; and forming an overcoat layer on the color filter layer.
 13. The method of claim 1, wherein the substrate is a plastic substrate.
 14. The method of claim 1, wherein the substrate is a flexible substrate.
 15. The method of claim 1, wherein the alignment material is formed of a polymer selected from polyimide, polyamic acid, polyvinylcinnamate, polyazobenzene, polyethyleneimine, polyvinylalcohol, polyamide, polyethylene, polystylene, polyphenylenephthalamide, polyester, polyurethane, or polymethylmethacrylate.
 16. The method of claim 1, wherein changing a field flux application direction is performed by rotating a field flux generator while maintaining the substrate stationary.
 17. The method of claim 2, wherein the electric field is applied by using an anode and a cathode coming into contact with both sides of the substrate. 